Hall effect keyer



Sheet of 3 @Mw A* ORNEYS June 10, 1969 R. H. TURJA HALL EFFECT KEYER Filed March 29, 1967 www,

June 10, 1969 R. H. TURJA HALL EFFECT KEYER Sheet Filed March 29, 1967 .v ...um

INVENroR RICHARD TUR/ United States Patent O 3,449,517 HALL EFFECT KEYER Richard H. Turia, Arlington, Va., assignor to Halliburton Company, Duncan, Okla., a corporation of Delaware Filed Mar. 29, 1967, Ser. No. 626,761 Int. Cl. H041 /04, 17/02 U.S. Cl. 178-79 14 Claims ABSTRACT OF THE DISCLOSURE A Hall elect telegraphic keyer including a Hall device held near and symmetrical with the small gap of a two pole permanent magnet, the Hall device being imbedded in a nonmagnetic support coupled to a spring-biased rocking toggle block assembly operated by a connector link of a tape reader, output current of said Hall device driving, according to mark and space shifts, a transistor bridge network controlling a gating transistor whose collector-emitter junction is in series with the output loop.

Background of the invention Conventional telegraphic keyers, such as used in tape readers, include a pair of fixed contacts with a rocker arm making electrical contact with each contact connected by means of a pivot to a tape reader link so that translatory motion of the link causes the rocker arm to rotate one direction or the other eiecting the make and break on the respective contacts. The rocker arm is mechanically biased in such a manner that it tends to return to the zero center position by action of a spring-biased contact finger exerting a known force on the contact arm so that resistance to link movement is no more than two ounces in the mark and space directions.

These conventional systems suffer from the disadvantage that when the mechanical contacts make and break slight but detectable arcing occurs resulting in noise generation on the output loop in addition to deterioration of the contacts which in turn increases the need for frequent maintenance servicing. Not only does this degenerate the information signals on the line but security becomes diicult to maintain because of the noise generation.

It is an object of the invention to avoid these problems mentioned above by providing a keyer which includes a Hall effect device arranged in a magnetic field, said device being moved by a tape reader line to control a transistor bridge network for Vthe production of corresponding mark and space voltages which are coupled to the control electrode of an output loop gating transistor.

It is a further object of the invention to provide a mechanical supporting and coupling assembly so that motion on the Hall device is compatible with the critical direction and pressure imparted and exerted by the conventional tape reader link. As is generally known, these tape reader links travel outward and inward from a zero position a distance of approximately 15 to 20 thousandths yof an inch in the mark and space directions respectively and requirements are such that the keying system imparts approximately two ounce resistance to tape reader link motion, to insure proper operation of the mechanical latches which serve as a memory to hold the operating 3,449,517 Patented June l0, 1969 Brief description of invention The Hall keyer of the invention includes a Hall device held near and symmetrical with the small gap of a twopole permanent magnet with a eld-concentrating plate covering the Hall plate on the opposite side from the magnet. A field-concentrator increases the density of the magnetic flux passing through the Hall device and also shields the Hall `device from external magnetic elds for enhancing signal reliability, and reducing susceptibility to interference from external sources. The Hall plate is held in a brass tube which is axially coupled to a conventional tape reader link `by a screw connector, which serves as a floating pivot. The screw connector is in t-urn movably held by a toggle block having each of its two legs resting against the guide edges of a cradle or anchor block assembly. This latter assembly is fitted with a tension spring extending parallel with the long axis of the toggle block and having one end connected to the anchor block and the other connected to the screw connector so that the toggle block always tends to return to the zero center position after the positioning force on the link is removed. The existing mechanical latches serve to hold the link in its last operated position (mark or space) until forcibly moved to the opposite position by subsequent action of the tape sensing mechanism. The combined action of the mechanical spring bias and the mechanical latches serves to provide mark and space positions of the link which can be accurately controlled with reliable repeatability, to avoid variable bias distortion of the signal. By means of mechanical coupling, the Hall plate is shifted to either one of two positions relative the magnet gap depending upon the action force on the link, Since the movement of the screw connector is slightly arcuate, play in the horizontal plane is provided in the tube guide block to prevent binding.

Another aspect of the invention is the circuit design which is controlled by the Hall device. Since the Hall device signal cannot directly drive the loop output transistor, a transistor bridge circuit is coupled between the Hall device output and the output loop keying transistor. The bridge circuit inherently balances and cancels out changes in transistor or component characteristics which may be caused by changes in temperature, humidity, supply voltage, etc. When the Hall device is at zero position, the output leads thereof have the same voltage potential thereon and the bridge transistors conduct equally, thus producing a bridge output of zero. But when the Hall device is moved to a mark or space position by the tape reader link, the bridge transistors are oppositely driven to near saturation and cutol conditions so that the bridge produces a plus or minus signal level accordingly. This signal is coupled to the output transistor control electrode to open or close the output loop thus producing corresponding mark and space conditions on the line. A silicon diode branch clamps one of the bridge transistors to prevent over driving the loop transistor. Various features of the circuit prevent transient and noise generation and provide the desired wave shaping for better telegraphic communication. The Hall device movement also enhances wave shaping.

Other and further advantages of the present invention will become apparent with the following detailed description when taken in view of the appended drawings in which:

FIGURE 1 is a side elevation, partially in section, of the device of the invention;

FIGURE 2 is a plan view of the device taken along line 2-2 of FIGURE l;

FIGURE 3 is a sectional view taken along line 3-3 of FIGURE 2;

FIGURE 4 is a sectional view taken along line 4 4 of FIGURE 2; J

FIGURE 5 is a plan view, partially in section of the Hall device support and toggle block assembly;

FIGURE 6 is a perspective view of the Hall device imbedded in a plastic envelope;

FIGURE 7 is a cross-section of the Hall device assembly taken along line 7-7 of FIGURE 5;

FIGURE 8 is a schematic view of the Hall device;

FIGURE 9 is an electronic diagram of a circuit, according to one aspect of the invention.

FIGURE 10 is an alternate output section of the circuit of FIGURE 9.

Detailed description of the embodiments of the invention With reference to the drawings, the Hall effect keyer comprises a Contact box generally indicated as 10 formed by a pair of outer box sections 12 and 14 each composed of material which shields magnet fields and held together by suitable means such as machine screw 16 and nut 18. A mounting bracket 20 cooperating with screw 16 secures contact box 10 to a suitable support near the Teletype reader. The mechanical mechanism housed within section 12 is mechanically coupled to the conventional tape reader apparatus by means of a conventional tape reader link 22. In order to be compatible with standard tape reader systems, link 22 must move in a translatory motion a distance of approximately to 20 thousandths of an inch from a referenced zero position and offer no more than two ounces of resistance in each direction. Section 14 -houses a printed circuit board with circuit components designed as described below.

In this example, section 12 houses the magnetic elements and Hall effect device as well as the supporting and guiding mechanism which includes a phenolic magnet mounting and guide block 24 securing a pair of two pole magnets 26 on a slab 28 of soft iron and in spaced relation generally as shown in FIGURES 2 and 4 so that the assembly forms a rigid U-shaped, two-pole magnet with north-south poles as indicated. The outer side of block 24 forms a guideway 30 extending transverse to the long dimension of the magnets and having a width less than the lengths of the magnets. It can be seen that the pole faces and gap therebetween are exposed at the bottom of guideway 30.

Mounting block 24 is secured to casing 12 by screw 16, nut 32, and Washer 31, and cooperates with the bottom wall of casing 12 to sandwich shims 34 therebetween. The purpose of shim 34 will be described herein below. The bore 36 through block 24 accommodating screw 16 is enlarged relative to the diameter of said screw so as to permit positioning adjustment of the block 24 and magnets 26.

The invention operates on the principle of moving a Hall device to either of two extreme positions in a magnetic field so as to intercept a number of flux lines with opposite resultant polarity according to the position of the device. Positioning, distances, directions and forces in the mechanism accomplishing such movement are critical to the accuracy, reliability and compatibility of the overall keyer arrangement. The invention achieves these standards by providing a swinging, spring biased toggle block assembly carrying a floating pivot screw 78 coupling the operating end of link 22 and an elongated tube 44 within which the Hall device is secured.

Considering rst the Hall device support, the Hall device 40 is imbedded in a plastic rectangular plate 42 in a position spaced near one end thereof. The long dimension of the Hall device extends transverse to the longitudinal axis of the plastic plate and the two control leads and two signal leads are connected in the standard fashion and extend toward the other end of the plate. One example of the Hall device is a thin wafer having a width of 0.060 inch when used with a magnet gap of 0.005 inch.

Plate 42 is secured with suitable epoxy cement to the outer surface of the base of a thin-walled, brass U-shaped channel 45. A magnetic field concentrator plate 46 of soft iron is fastened with epoxy cement to the inner sur face of the base of the U-shaped channel, positioned opposite and symmetrical to the Hall device 40. This assembly comprising the U-shaped channel 45, plate 42 and flux concentrator 46 is then inserted and cemented inside a thin-walled, square cross-section, brass tube 44. Concentrator plate 46 serves to intensify and normalize the magnetic flux passing through the Hall device 40 and also to minimize the effects of stray extraneous magnetic elds and avoid the generation of erroneous signals. When the U-channel assembly is positioned inside the square brass tube 44, the Hall plate 42 will thus be sandwiched between the base wall of the U-channel and one wall of the square tube. The U-channel and square tube have thin walls (about 0.005 inch thickness) in order to introduce a minimum gap in the magnetic circuit. This type of assembly provides effective electro-static shielding of the Hall element and also protects it from physical damage. The open ends of tube 44 are sealed with a suitable epoxy which also partially fills the interior of tube 44 and covers leads 41, plate 42 and the field concentrator 46. Tube 44 is partially filled with epoxy so as to keep the mass and inertia thereof low. One end of tube 44 is secured to pivot link 88 which cooperates with pivot screw 78. The dimensions of concentrator plate 46 are sufficient to assure plate overlap of device 40 on all sides.

When assembled, tube 44 reciprocally rides in guide slot 30 in block 24 oriented with device 40 facing magnets 26 and positioned with its width symmetrical to the magnet gap as seen in FIGURES 1, 2 and 4. For reasons mentioned below, the width of channel 30 is slightly greater than the outer width dimension of tube 44.

In order to prevent vertical displacement of tube 44 from guide 30, a phenolic plate 48 covering a liner 50 preferably made of Teflon is secured to the face of block 24 by brass screws 52 and 54. Teon liner 50 serves to engage the top side of tube 44 and prevent binding and reduce resistance to tube motion.

As mentioned, the supporting and resistance characteristics of the toggle mechanism are important. According to the invention, mark and space translatory motion is imparted to tube 44 by means of a toggle assembly pivotly coupling tube 44 to the operating end of the link 22. The toggle block 72 rides between upper and lower guide plates 58 and 86 held by screws 60 to restrict the vertical motion. The under side of lower plate 58 is counterbored and positioned flat against the bottom of the casing. As can be seen, the counterbores provide spaces for the parts of threaded bushings 61 penetrating the casing and serving to receive screws 60. Anchor block 64 is sandwiched between guide plates 58 and 86 and is provided with a pair of openings 66 accommodating screws 60. The anchor block 64 includes a pair of projections 68 the inner surfaces of which slope outward and away from the restraining surface 70 of the block. The assembly further includes a toggle block 72 provided with a pair of legs 73 and 74 separated by an arcuate side 76, said legs -being spaced so that toggle lblock 72 is cradled -with legs 73 and 74 fitting at the junction of the projection 68 and back surface 70.

The pivot screw 78 is threaded into a projecting ear 80 at the opposite end thereof from legs 73 and 74 of toggle block 72. Mark and space translations of link 22 effect a corresponding horizontal rocking motion of toggle block 72 about either leg 73 or 74 depending upon direction. Such rocking occurs with minimum friction by virtue of the knife edge type support. In order to bias toggle block 72 and pivot 78 toward a zero center position and further to offers the required amount of resistance to motion, there is provided a tension spring 82 having one end held by a securing pin 84 in anchor 64 and the other end coupled to pivot screw 78 by means of solder lug l85. Spring 82 passes through hole 65 in anchor block 64 and through hole 73 in toggle block 72 as best seen in FIGURE 5. Thus, with tension spring 82 aligned along the length of toggle block 72, further tensioning of spring 82 occurs with the horizontal motion of the pivot 78 away from center. Spring 82 in cooperation with legs 73 and 74 provide vertical support for the moving parts of the toggle assembly. The spring constant for and length of spring 182 should be selected to provide the desired forces on link 22 during operation in view of the masses and dimensions of the various moving elements of the assembly.

Pivot screw 78 further carries a pair of centrally abutting flanged collars 79 (FIGURE 4) which in turn act as a bearing surface for the brass tube pivot link 88 and the operating end of link 22. In this way, tube 44, link 22 and toggle block 72 pivot relative to each other about screw 78 which during motion travels in a slight arc about either leg 73 or 74 depending upon direction.

In operation, link 22 coupled to conventional tape reader machine causes link translation with a pushing motion for mark and a pulling motion for space relative to a zero center position. It should be remembered that the tape read apparatus permits link 22 to rest in only one of two off-center positions but by virtue of spring 82, the force on link 22 is always toward a zero center position. The translation distance from center is to thousandths of an inch from a zero set and there can 'be no more than two ounces of resistance offered by the keyer mechanism. As link 22 translates, pivot screw 78 moves accordingly thus causing translation of tube 44 in guide 30 and rocking of toggle block 72 about legs 73 or 74 depending upon direction. As one of these legs lifts away from surface 70, tension is increased on spring 82 so that when the driving force is removed, spring 82 tends to return toggle block 72 toward a zero center position and link 22 and tube 44 tend to return to their zero center positions accordingly.

The Hall device action in the magnetic field is better seen in FIGURE 4. In that figure, when tube 44 moves to the mark position, Hall device 40 and field concentrator 46 move to the left so that a major sensitive portion of the device lies over the north pole. A corresponding voltage is developed on the signal output leads of the Hall device to control the loop signal in the manner described below. When tube 44 is pulled to the right, Hall device 40 translates accordingly and becomes offset toward the south pole, thus producing a corresponding voltage on the signal output leads. The final positions for mark and space are symmetrical with the pole gap. The field concentrator 46 not only protects the Hall device 40 from extraneous external fields which may produce erroneous signals but in addition, it maintains the flux lines in the immediate vicinity of Hall device 40 more perpendicular to the plane of device 40.

Because of the finite time necessary for displacement of the Hall device and smooth motion acceleration and deceleration thereof, the leading and trailing edges of the Hall device output signal are properly shaped with noise and transient effects minimized.

With reference to FIGURE 9, there is illustrated the circuit responding to the VHall device signals for generating the telegraphic loop signals. The circuit includes a transistor bridge circuit producing control mark space voltages in response to the Hall device output signals and feeding the control voltage to an output loop gating transistor for developing mark and space signals on the line. In detail, there is provided a control power supply 101 feeding the control current electrodes 100 and 1012 of the Hall device 40 through a current limiting resistor 104. In one example, the values are chosen so that the control current through the Hall device is milliamps. The Hall device output leads 106 and 108 `feed a transistor bridge circuit 110 which in turn controls a gating transistor l112 whose collector-emitter electrodes are connected in series with the output telegraphic loop.

The bridge circuit includes a matched pair of transistors 114 and 116 of the same conductivity type, in this case NPN, each having an emitter connected to one of the output leads 106 and 108 respectively. Equal valued load resistors 118 and 120 connect the respective collectors of transistors 114 and 116 to the positive terminal of control voltage source 101. The bases of transistors 114 and 116 are mutually coupled through a bias resistor 122 to the positive terminal of control voltage source 101, and in one example, the bias resistor 122 has a value 100 times the resistor 118 or 120.

The output of the bridge circuit is taken at collector terminals 123 and 125 and fed by leads 124 and 126 to the emitter-base electrodes of gating transistor 112. When the Hall device 40 moves to the mark position, transistors 114 and 116 are driven near cutoff and saturation, respectively, thus increasing the positive voltage Iat terminal 123 relative terminal 125 which ultimately drives transistor 112 to near saturation. A diode clamping circuit comprising a number, for example three, silicon diodes limits the voltage at terminal 123 to a suitable value, such as 1.8 volts, to prevent overdriving transistor 112 and to reduce noise and transients in the control signals. Resistors 142 and 144 in series with the base of transistor 112 further limit the drive current fed thereto.

At the gating and output circuit, a standard external loop battery feeds the line through series current limiting resistors 136 and 138. Capacitor 134 is coupled from collector to base of transistor 112 to provide wave shaping and RFI reduction. Further precaution is taken to prevent deep saturation of transistor 112 by coupling silicon diode from the collector to the common connection of resistors 142 Iand 144. Diode 140 is forward biased only when transistor 112 reaches the threshold of saturation. Diode 132 connected across the base-emitter electrodes of transistor 112, but poled oppositely thereto, serves to match the load condition on the bridge during space generation with the load condition on the bridge during mark generation. Diode 132 further serves to prevent the bridge circuit from going into oscillation.

For better understanding of the circuit operation, if during testing the voltage potential difference between leads 106 and 108 is zero, the bridge circuit is balanced so that transistors 114 and 116 conduct equally causing a zero potential difference to appear on bridge output leads 124 .and 126. During normal operation, either a mark or space voltage of opposite polarity is generated from Hall device 40. When a mark signal is generated by Hall device 40, lead 106 becomes negative relative to lead 108 and transistor 116 increases conduction to near saturation and transistor 114 decreases conduction to near cutoff so that lead 124 becomes positive relative to lead 126. Clamping circuit 130 clamps the mark output signal to plus 1.8 volts which back biases diode 132 and drives transistor 112 to the saturation threshold by supplying base drive current through resistors 142 and 144. This action of transistor 112 closes the output loop placing a mark signal on the line which is properly shaped by action of capacitor 134. As transistor 112 reaches the threshold saturation, diode 140 clamps the base-collector voltage to a desired level thus preventing deep saturation.

When a space signal is generated by Hall device 40, transistor 114 conducts near saturation and transistor 116 drops to near cutoff in which case clamping circuit 130 is back biased, the respective voltage polarity on leads 124 and 126 is minus causing diode 132 to conduct and back biasing transistor 112 to assure complete cutoff and thus placing a space signal on the line. One example of the invention comprises components as follows.

Transistors 112, 114, 116 2N929 Hall device control current ma 100 Control voltage source v 6.8 Ext. loop battery v 6.0

Resistors (all 1/4 watt, 5%):

104 ohms-- 68 118, 120 do 6.8K 122 1 do 680K 136, 138 do 47 142 1 do 150K 144 1 do 220K Diodes:

130 (each) 1N645 132 1N645 140 1N645 Capacitor 134 pf 270 1Values for these resistors are approximate. Final values should be selected in each case to match transistor characteristics for minimum radio frequency interference with suitable output waveform.

Thus, there has been described one embodiment of a Hall effect keyer having a unique supporting and moving mechanism rendering the keyer completely compatible with conventional tape reader systems and in addition which includes a bridge circuit for controlling the output loop transistor for the generation of mark and space s1gnals on the line. Various modifications can be made to the herein disclosed example of the present invention without departing from the spirit or the scope thereof. For example, the circuit as disclosed is suitable for NEU- TRAL operation but the circuit can be adapted for POLAR operation by replacing diode 132 with a complementary second gating transistor and connecting the POLAR output loop as illustrated in FIGURE 10 where like characters refer to like components. For MARK generation, transistor 112 is conducting and transistor 150 is nonconducting. The load current feeds through load resistor 152 from left to right in the ligure. During space generation, transistors 112 and 150 are nonconducting and conducting, respectively, and current passes through load resistor 152 from right to left in the figure.

What is claimed is:

1. A Hall effect telegraphic keyer including a contact box, a permanent magnet held within said contact box establishing a magnetic eld therein, a Hall device with two control leads 4and two output leads connected thereto, a toggle assembly held in said contact box including a nonmagnetic support to which said Hall device is secured, said support arranged to position said Hall device in a predetermined relation within said magnetic field and mounted for movement in a predetermined direction relative to said magnet, a tape reader connecting link arranged for translatory mark-space displacements effected by ya conventional tape reader, said link being coupled to said toggle assembly for moving said support in alignment with said guide so that said Hall device moves between mark-space positions accordingly in said magnetic eld, means for supplying a predetermined control current to said Hall device control electrodes so that markspace signals are generated on the output leads when the Hall device is in the respective position, a telegraphic output loop completed through a controlled electronic gating element effecting mark-space signals on the output loop depending upon its conductive condition, an electronic circuit for controlling the gating element in response to the output signals of said Hall device.

2. A keyer as set forth in claim 1 wherein said toggle assembly includes biasing means for biasing the link and support toward respective center positions, said biased toggle assembly imparting less than .a predetermined amount of resistive force to the motion of said link.

3. A keyer as set forth in claim 2 wherein said assembly includes an anchor block secured to the contact box, an elongated toggle block in floating contact with said anchor block and Iarranged for rocking movement thereon, a pivot carried by a part of said toggle block spaced from said anchor block, said link and support coupled to said pivot, at least two of said toggle block, link and support being rotatable on said pivot so that translatory movement of said link causes rocking of said toggle block on said anchor block and movement of said support.

4. A keyer as set forth in claim 3 wherein said support is elongated and is guided in alignment with the translation of said link, the direction between said anchor block and pivot being generally perpendicular to the direction of link translation, the mutually contacting parts of said anchor block and toggle block forming a pair of knife edge supports spaced in direction of link motion about one of which said toggle block rocks depending upon direction of link movement, said biasing means urging the lassembly toward a position in which both said knife edge supports contact said anchor block.

5. A keyer as set forth in claim 4 wherein said biasing means comprises a spring tensioned from said pivot to said anchor block and extending between the pair of knife edge supports.

6. A keyer as set forth in claim 1 wherein said support comprises an elongated tube-like member of nonmagnetic material, said Hall device being imbedded in a nonmagnetic plate which is carried by said member, said magnet comprising two poles with a magnet gap therebetween, said gap extending transverse to the guided direction of Hall device movement, said Hall device and magnet arranged so that when in the center position, the Hall device is symmetric to the gap and no signal is generated at the output leads.

7. A keyer as set forth in claim 6 wherein a field concentrator plate formed of magnetic material is provided on the side of the Hall device opposite the magnet poles for blocking external or extraneous fields from the device and for normalizing the field ux lines, said concentration plate overextending all edges of said Hall device.

8. A keyer as set forth in claim 3 wherein a guide means guides the movement of said support in a direction generally perpendicular to the gap between magnet poles and said guide means permitting a small displacement of the support in the direction parallel to the magnet gap so as to accommodate for the arcuate movement of the pivot.

9. A keyer as set forth in claim 1 wherein electronic element comprises a gating transistor with its collector and emitter electrodes coupled in series with the output loop and a control electrode coupled to the circuit, said circuit including means to limit the drive current supplied to said control electrode.

10. A keyer as set forth in claim 9 wherein said circuit includes a normally balanced transistor bridge circuit with a pair of output terminals directly coupled to said gating transistor, said circuit including a pair of transistors of same conductivity type biased and coupled to the Hall device output leads such that one conducts near cutoff and the other conducts near saturation threshold in response to a mark or a space signal from the Hall device.

11. A keyer as set forth in claim 9 wherein first means yare connected to said gating transistor for preventing the same from going into deep saturation and second means are connected to said gating transistor for reducing the noise content of the loop signal.

12. A keyer as set forth in claim 10 wherein a device is coupled across said pair of output transistor bridge terminals for completing the current path therebetween when said gating transistor is turned off.

13. A keyer as set forth in claim 10 wherein said means to limit the drive current includes a diode clamp connected to one of the bridge output terminals and a current limiting resistor connected in series with the gating transistor control electrode, there also being provided a clamping diode coupled to one of the collector-emitter electrodes and the control electrode to prevent the gating transistor conduction near threshold level, a diode connected from the other of the collector-emitter electrodes to the control electrode for providing a shunt current path when the gating transistor is back biased, and a feedback capacitor connected to two of the gating transistor electrodes for reducing noise in the output signal and shaping the same.

14. A keyer as set forth in claim 10 wherein the pair of bridge transistors have corresponding electrodes cou- References Cited UNITED STATES PATENTS 10/1959 Abraham.

7/1966 Weiss.

THOMAS A. ROBINSON, Primary Examiner.

M. M. CURTIS, Assistant Examiner.

U.S. C1. X.R. 

